Method for manufacturing a dual chip in package with a flip chip die mounted on a wire bonded die

ABSTRACT

A method for creating a die that has some bond pads that are compatible with wire bonding and others that are compatible with solder bonding. A layer of copper is disposed over aluminum bond pads and selectively removed from those bond pads that are desired to be compatible with wire bonding.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to semiconductor packaging. Morespecifically, the invention relates to the design and manufacturingprocess of a semiconductor package that allows the incorporation of morethan one chip device into a single package.

2. Description of the Related Art

For a variety of reasons well known in the art, semiconductor packagesthat have more than one chip, otherwise known as multi-chip modules(“MCM's”), are becoming increasingly popular. One type of possible MCMis shown in FIG. 1, which is disclosed in U.S. patent application Ser.No. 09/461,704, entitled “Multi-Chip Package Including Memory andLogic,” filed Dec. 14, 1999, and is owned by the assignee of the presentinvention. The MCM shown in FIG. 1 comprises a top die 10 stacked on topof a bottom die 12, which is in turn mounted on a substrate 18. The topdie 10 is mounted on the bottom die 12 in flip chip fashion such thatthe top die 10 communicates with the bottom die 12 through a pluralityof (collapsed) solder balls 20. The bottom die 12, in turn, communicateswith the substrate 18 through a plurality of wires 14. Thus, the bottomdie 12 has two types of bond pads: flip-chip bond pads that are coupledto a plurality of solder balls 20 and wire bond pads that are coupled tothe plurality of wires 14.

Both types of bond pads are aluminum. Aluminum bond pads form effectivebonds with the plurality of wires 14. However, the aluminum bond padsmay not effectively bond to the plurality of solder balls 20, whichoften comprise eutectic solder (e.g., 63% Sn/37% Pb). The mismatchbetween the different types of bonding, solder ball and wire bond, makesit somewhat difficult to manufacture the package shown in FIG. 1. Itwould be desirable to improve the efficiency of the manufacturingprocess for a package such as that shown in FIG. 1.

SUMMARY OF THE INVENTION

To achieve the foregoing, the present invention provides a method formanufacturing a die comprising two different types of bond pads, onetype that is compatible with wire bonding and another type that iscompatible with solder bonding. In one embodiment, the bond pads thatare compatible with wire bonding have a top layer of aluminum while thebond pads that are compatible with solder bonding have a top layer ofcopper.

All of the bond pads can initially consist of aluminum. To selectivelyform copper over the solder compatible bond pads, a layer of copper isdisposed over all the bond pads and selectively etched away from overthe wire bonding compatible bond pads. The copper can be selectivelyetched by disposing a layer of photoresist over the copper, removing thephotoresist from over the wire bonding compatible bond pads, and thendissolving the copper in a suitable solution. The solution, dissolvedcopper and remaining photoresist are then removed, thereby leavingcopper over the solder compatible bond pads while returning the wirebonding compatible bond pads to aluminum without an overlay of copper.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a flip-chip on wire bond multi-chipmodule package.

FIGS. 2a-2 f are sectional views, not to scale, illustrating successivesteps, according to the teachings of the present invention, in thepreparation of a die that may be used in a package such as that shown inFIG. 1.

FIG. 3 is an expanded cross section view of under the bump metallurgyshown diagrammatically in FIGS. 2b-2 f.

FIGS. 4a and 4 b, respectively, show possible steps for flip chipmounting a top die on a bottom die that has been processed in accordancewith FIGS. 2a-2 f.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Definitions

A material or other item is said to be “over” a bond pad when a linethat is normal to the surface of the bond pad passes through thatmaterial or item. Thus, a material or item may be “over” a bond padwithout being on the bond pad.

A “solder compatible material” is a material that bonds with solder whenthe solder is melted at temperatures above 183° C.

FIGS. 2a-2 f are sectional views, not to scale, illustrating successivesteps, according to the teachings of the present invention, in thepreparation of a die that may be used in a package such as that shown inFIG. 1. However, it will be appreciated that the present invention isnot limited to constructing packages identical to those in FIG. 1.

As shown in FIG. 2a, a semiconductor die 30 comprises a first bond pad32 and a second bond pad 34, each of which consists of aluminum. Thefirst bond pad 32 and the second bond pad 34 may comprise other wirebond compatible materials, including, without limitation, aluminumalloys. For the purposes of clarity, only two bond pads are shown but itwill be appreciated that more than two bonds are usually present onsemiconductor dies such as the die 30. It is desired to make the firstbond pad 32 compatible with wire bonding and the second bond pad 34compatible with flip-chip type bonding. “Under bump metallurgy” 36,comprising nickel, vanadium and copper, is deposited on the first bondpad 32 and the second bond pad 34, as shown in FIG. 2b. One suitableunder bump metallurgy process is performed by Flip Chip TechnologiesInc. FIG. 3 is an expanded cross section view of the under bumpmetallurgy 36. As shown in the Figure, a layer of copper 35 overlies alayer of vanadium 37, which in turn overlies a layer of nickel 39. Thus,referring back to FIG. 2b, copper is now the top layer on the first bondpad 32 and the second bond pad 34. Although copper is the preferred toplayer material for the second bond pad 34, it will be appreciated thatother solder compatible materials may be employed, including, withoutlimitation: Cu—Ni/Au.

Next, a layer of photoresist 38 is disposed over the first bond pad 32and the second bond pad 34 and the remainder of the top layer of the die30, as shown in FIG. 2c. As shown in FIG. 2d, the first bond pad 32 isexposed by creating a hole 39 in the photoresist 38 over the first bondpad 32. The hole 39 may be created in many ways. In one embodiment, thehole 39 is created by employing well known lithography/etch techniquesused widely in semiconductor manufacturing. In particular, the topsurface of the die 30 is masked with a pattern, the mask/die 30 assemblyis exposed to light (lithography), the photoresist 38 is developed andthen selectively etched.

As shown in FIG. 2e, the under bump metallurgy 36 over the first bondpad 32 is etched away by immersing the die 30 in an appropriate solutionsuch as Hydrofluoric acid, which does not dissolve aluminum, and thenremoving the solution with the dissolved under bump metallurgy. However,Hydrofluoric acid can be very harmful, and appropriate precautionsshould be taken.

As shown in FIG. 2f, the photoresist 38 is removed. The under bumpmetallurgy 36 is the top most layer over the second bond pad 34 whilealuminum is the top most layer over the first bond pad 32. A packagesuch as that shown in FIG. 1 may now be readily assembled with the die30 used as the die 12.

FIGS. 4a and 4 b, respectively, show possible steps for flip chipmounting a top die 60 on a bottom die 62 that has been processed inaccordance with FIGS. 2a-2 f. As shown in FIG. 4a, the bottom die 62 hasa first plurality of bond pads 64 and a second plurality of bond pads66. The first plurality of bond pads 64 include aluminum such as thebond pad 32 shown in FIG. 2f while the second plurality of bond pads 66has under bump metallurgy disposed thereon such as the bond pad 34 shownin FIG. 2f.

As shown in FIG. 4a, the top die 60, which has a plurality of solderbumps 68 on each of a third plurality of bond pads 72, is placed on thefirst die 30 such that each of the solder bumps 68 is bonded with acorresponding one of the second plurality of bond pads 66. Typically,the process of bonding the solder bumps 68 to the second plurality ofbond pads 66 involves disposing flux on the solder bumps 68, placing thetop die 60 on the bottom die 64 such that each of the solder bumps 68contacts a corresponding one of the second plurality of bond pads 66,and then heating the resulting assembly. The solder bonding process iswell known and will not be further discussed; any suitable solderbonding process may be employed. For example, an alternative methodinvolves placing solder bumps directly on each of the second pluralityof bond pads 66 and then disposing the top die 60 on the bumped bottomdie 62.

After the top die 60 has been flip-chip mounted to the bottom die 62,each of a plurality of wires 70 is wire bonded to a corresponding one ofthe first plurality of bond pads 64, resulting in a package such as thatshown in FIG. 1.

Although the foregoing invention has been described in detail tofacilitate an understanding thereof, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims.

What is claimed is:
 1. A method for rendering a first semiconductor diecompatible with both wire bonding and solder bonding, the firstsemiconductor die comprising a top surface with a first bond pad and asecond bond pad thereon, wherein the first and second bond pads eachcomprise a wire bond compatible material, the method comprising thesteps of: disposing a solder compatible material over the first bond padand the second bond pad, wherein the wire bond compatible materialremains intact on the first and second bond pads; and removingsubstantially all of the solder compatible material over the first bondpad such that the wire bond compatible material on the first bond pad isexposed and substantially all of the solder compatible material remainsover the second bond pad.
 2. The method of claim 1 wherein the solder iseutectic solder.
 3. The method of claim 1 wherein the wire bondcompatible material comprises aluminum.
 4. The method of claim 1 whereinthe solder compatible material comprises copper.
 5. The method of claim1 further comprising the step of disposing a third material over thefirst bond pad and the second bond pad before the step of disposing thesolder compatible material over the first bond pad and the second bondpad.
 6. The method of claim 5 further comprising the step of disposing afourth material on the first bond pad and the second bond pad before thestep of disposing the solder compatible material over the first bond padand the second bond pad.
 7. The method of claim 6 wherein: the soldercompatible material consists of copper, the third material consists ofvandium and the fourth material consists of nickel.
 8. The method ofclaim 1 wherein the step of removing the solder compatible materialcomprises the step of dissolving the solder compatible material in asolution.
 9. The method of claim 8 wherein the step of dissolving thesolder compatible material in a solution comprises the steps of:disposing photoresist over the solder compatible material that is overthe first bond pad and the second bond pad; removing the photoresistfrom the solder compatible material that is over the first bond pad,thereby exposing the solder compatible material that is over the firstbond pad; and after the step of removing the photoresist, exposing thesolder compatible material that is over the first bond to the solution.10. The method of claim 1 wherein: the step of disposing a soldercompatible material over the first bond comprises the step of disposingthe solder compatible material over a first plurality of bond pads and asecond plurality of bond pads; and the step of removing substantiallyall of the solder compatible material over the first bond pad comprisesthe step of removing substantially all of the solder compatible materialover the first plurality of bond pads such that substantially all of thesolder compatible material remains over the second plurality of bondpads.
 11. A method for manufacturing a semiconductor package comprisinga first semiconductor die and a second semiconductor die, the firstsemiconductor die comprising a top surface with a first bond pad and asecond bond pad thereon, wherein the first and second bond pads eachcomprise a wire bond compatible material, the second semiconductor diehaving a third bond pad on its active surface, the method comprising thesteps of: disposing a solder compatible material over the first bond padand the second bond pad, wherein the wire bond compatible materialremains intact on the first and second bond pads; removing substantiallyall of the solder compatible material over the first bond pad such thatthe wire bond compatible material on the first bond pad is exposed andsubstantially all of the solder compatible material remains over thesecond bond pad; mounting the second semiconductor die on the first diesuch that the third bond pad on the second semiconductor die is bondedto the second bond pad by solder; and wire bonding a wire to the firstbond pad.
 12. The method of claim 11 wherein the solder is eutecticsolder.
 13. The method of claim 11 wherein the wire bond compatiblematerial comprises aluminum.
 14. The method of claim 11 wherein thesolder compatible material comprises copper.
 15. The method of claim 11further comprising the step of disposing a third material over the firstbond pad and the second bond pad before the step of disposing the soldercompatible material over the first bond pad and the second bond pad. 16.The method of claim 15 further comprising the step of disposing a fourthmaterial on the first bond pad and the second bond pad before the stepof disposing the solder compatible material over the first bond pad andthe second bond pad.
 17. The method of claim 16 wherein the soldercompatible material consists of copper, the third material consists ofvanadium and the fourth material consists of nickel.
 18. The method ofclaim 11 wherein the step of removing the solder compatible materialcomprises the step of dissolving the solder compatible material in asolution.
 19. The method of claim 18 wherein the step of dissolving thesolder compatible material in a solution comprises the steps of:disposing photoresist over the solder compatible material that is overthe first bond pad and the second bond pad; removing the photoresistfrom the solder compatible material that is over the first bond pad,thereby exposing the solder compatible material that is over the firstbond pad; and after the step of removing the photoresist, exposing thesolder compatible material that is over the first bond to the solution.20. The method of claim 11 wherein: the step of disposing a soldercompatible material over the first bond comprises the step of disposingthe solder compatible material over a first plurality of bond pads and asecond plurality of bond pads; and the step of removing substantiallyall of the solder compatible material over the first bond pad comprisesthe step of removing substantially all of the solder compatible materialover the first plurality of bond pads such that substantially all of thesolder compatible material remains over the second plurality of bondpads.
 21. A method for rendering a first semiconductor die compatiblewith both wire bonding and solder bonding, the first semiconductor diecomprising a top surface with a first bond pad and a second bond padthereon, wherein the first and second bond pads each comprise a wirebond compatible material, the method comprising the steps of: disposinga solder compatible material over the first bond pad and the second bondpad; removing substantially all of the solder compatible material overthe first bond pad such that substantially all of the solder compatiblematerial remains over the second bond pad; and disposing a thirdmaterial over the first bond pad and the second bond pad before the stepof disposing the solder compatible material over the first bond pad andthe second bond pad.